1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy, and more particularly, to an alkali metal electrochemical cell having a positive electrode comprising a cathode active admixture of a metal-containing material combined with fluorinated carbon.
Advantages related to the use of a metal-containing material/fluorinated carbon admixture include increased capacity during high rate discharge applications. An example of such an application is the implantable cardiac defibrillator where the electrochemical cell may discharge under a light load for extended periods of time interrupted by high rate pulse discharge. Utilizing a mixture of a metal-containing material such as a metal, a metal oxide, a mixed metal oxide or a metal sulfide and fluorinated carbon provides a blend of the high power density of the metal material and the high capacity associated with the fluorinated carbon to give a cathode active material admixture displaying enhanced performance exceeding either of the independent materials.
2. Prior Art
The use of a metal-containing material such as a mixed metal oxide containing copper, silver and vanadium (Cu.sub.x Ag.sub.y V.sub.2 O.sub.z, CSVO) has been previously demonstrated for application as a cathode active material in an alkali metal electrochemical cell. For a thorough discussion of the preparation of CSVO, reference is made to U.S. Pat. No. 5,472,810 to Takeuchi et al., which is assigned to the assignee of the present invention and incorporated herein by reference. In addition to having a high energy density, the use of CSVO cathode active material in an alkali metal electrochemical cell provides a high delivered capacity for the intercalation of the alkali metal under high rate applications. Likewise, the use of fluorinated carbon (CF.sub.x).sub.n has also been previously demonstrated for cathodes in primary lithium batteries (Linden, D. Handbook of Batteries & Fuel Cells; McGraw Hill: New York, 1984; p. 11-55). Fluorinated carbon generally is used in low to medium rate applications where high power density is not required.
U.S. Pat. No. 5,180,642 to Weiss et al. discloses electrochemical cells having a cathode mixture comprising carbon monofluoride and a minor amount of an additive such as vanadium oxide and silver vanadate. This patent is directed to the combination of these materials as an end-of-service indication and not to the formulation of a blended cathode material for both light load and high pulse discharge applications.
U.S. Pat. Nos. 5,273,846 to Plichta et al., 4,707,422 to de Neufville et al., 4,316,777 to Dey and 4,670,363 to Whitney relate to combining a metal oxide with a carbonaceous cathode active material; however, they do not discuss the use of such a mixture for both light load discharge and current pulse discharge applications.